1. Field of the Invention
The present invention relates to an ink jet printer and particularly to a printing head protecting device used in the same.
2. Description of the Prior Art
In conventional drop on-demand type ink jet printers it is required to keep narrow and constant the spacing between the ink jet surface of a printing head and a printing paper. But if this spacing is made narrow, the paper when floated from the platen surface may contact the ink jet surface while the latter is moving for printing, and damage of the printing head may result. This danger may be averted by the provision of a protective plate at a side portion of the ink jet surface so that the protective plate projects slightly from the ink jet surface. In on-demand type ink jet printers there is known the so-called purging technique (see Japanese Patent Laying Open Print No. 150030/1977) in which a cleaning roller for removing air bubbles formed within an ink jet chamber and for cleaning the ink jet surface is disposed in an end position of a reciprocating path of a printing head, the printing head is moved to a position opposed to the cleaning roller and a relatively large amount of ink is jetted toward the same roller to form an ink column between the printing head and the cleaning roller, then this ink column is removed. In this case, the spacing between such cleaning roller and the ink jet surface of the printing head is set narrower than the foregoing spacing between a printing paper and the ink jet surface, therefore in case the printing head provided with a protective plate is moved so as to be opposed to the cleaning roller, the protective plate must be retreated in advance, or else the protective plate may strike the surface or a side of the roller thus resulting in a possible damage of the roller or the protective plate. Therefore, it is necessary for the protective plate to be sure to project when the printing head is opposed to the platen and retreat when the printing head has moved toward the roller.